The S5700 switch periodically selects a different NTP server and a big number of NTP/4/PEER_SELE logs are recorded in the logbuffer

Publication Date: 2016-11-30Views: 1820Downloads: 0

Issue Description

Scenario:

A S5700 switch is configured to synchronize with 3 NTP servers. In the logs it can be observed that the switch is frequently changing the NTP server and a big number of NTP/4/PEER_SELE logs are occupying the logbuffer memory.

Logs:

Nov 7 2016 05:24:48+11:00DST S5700 %%01NTP/4/PEER_SELE(l)[20]:The peer selected by the system is xx.xx.65.254.

Nov 7 2016 03:26:33+11:00DST S5700 %%01NTP/4/PEER_SELE(l)[21]:The peer selected by the system is xx.xx.140.38.

Nov 7 2016 02:53:10+11:00DST S5700 %%01NTP/4/PEER_SELE(l)[22]:The peer selected by the system is xx.xx.129.130.

Configuration :

ntp-service source-interface Vlanif1

ntp-service unicast-server xx.xx.129.130 authentication-keyid 1

ntp-service unicast-server xx.xx.140.38 authentication-keyid 1

ntp-service unicast-server xx.xx.65.254 authentication-keyid 1

Solution

By default,in the unicast-server mode,the polling mechanism of the NTP client is sending a NTP message to each of the configured servers every 64 seconds. When the client receives the replies from the server, it will choose a peer depending on a number of factors(small, stratum, nearest, most accurate, delay) . In the situation where the replies received from the servers are similar, the switch needs to select onlyone server from which to synchronize its time. If its decision differs from the previous one, a log will be recorded in the log buffer.

In order to avoid the described situation,
in the case where have multiple NTP servers, we would need to indicate one of
the servers as the preferred one by making use of the “preference” parameter with the ntp-service
unicast-serverip-address command . In this way, the NTP server will
no longer be elected by chance and we will have a stable NTP service.